1. Field of the Invention
The present invention relates to a method for preservation and/or modification treatment of wood. More particularly, it relates to a method for making wood moth-resistant, moisture-resistant, and/or fire-resistant, through impregnation of the fibers with chemicals such as preservatives, mothproofing agents, fire retardant, modifiers including polyethylene glycol, synthetic resins, and the like.
2 Description of the Prior Art
Development of methods for preservation treatment of wood has increased usefulness of wood as a structural material for interior construction such as interior walls, flooring and the like. The preservation treatment is generally carried out by dipping wood in a preservative solution, accompanied by vacuum impregnation and/or pressure impregnation. It is, however, difficult to produce uniformly treated wood because of differences in the rate of penetration of a preservative between two parts of the main stem of a tree, i.e., the outer part (sapwood portion) and the inner core (heartwood portion).
Penetration of preservative may be improved by incising, i.e., by mechanically making spaced slitlike cuts in the outer layer of wood with an incising machine. The incising is not so effective for large logs or square timber of with large size as it can only provide shallow holes. Since the heartwood is generally penetrated with the preservative at a low rate as compared with the sapwood, the preservation treatment of heartwood takes a long period of time even if the wood to be treated has been incised before preservation treatment.
The preservation treatment of wood is generally accomplished by artificial drying procedures such as heating the wood with steam or hot air, and dielectric heating resulting from application of high frequency waves, to finish the drying process within a short time. The artificial procedures increase the rate of drying as compared with natural air drying, but there are some problems awaiting a solution. For example, the steam or hot-air drying is accompanied by rapid surface drying, and heating due to conduction of heat, so that the water in the outer portion of the wood is discharged easily by evaporation. However, the moisture movement in the inner portion is very low as compared with that in the outer portion, so that a difference in the moisture content between the outer and inner portions of the wood is produced during drying, which may cause surface cracking, inter checks or other defects during drying process, and by twist, crook cupping and other defects after drying. To avoid these problems, it is required to lower the rate of drying, thus making it difficult to reduce the time for drying.
In dielectric heating, the interior of wood is heated simultaneously with the outer portion, but the moisture contained therein is removed through the wood by diffusion. Thus, if the wood is heated under severe conditions, it may degraded by cracking due to difference in the moisture content between the inner and outer portions.